In a cellular wireless communication system, when a channel condition is degraded due to a geographical factor within a cell, a distance between a terminal and a base station, and a movement of a terminal, a failure of the smooth communication between the terminal and the base station may be generated. For example, within a closed building, such as an office and a house, a radio wave shadow area is created and a base station cannot perform the smooth communication with a terminal located in the radio wave shadow area.
Accordingly, the wireless communication system provides a femtocell service for providing high-speed data service while solving a service problem in a radio wave shadow area. The femtocell means an area of a cell relatively smaller than the macrocell and is formed by a femto base station installed in a region desired by a user. That is, the femtocell is a micro mobile communication base station accessing a mobile communication core network through a broadband network installed inside a building, such as a house and an office. The femtocell is a compound word of a “femto” meaning 10-15 and a “cell” meaning a coverage area of a mobile phone, and means a base station capable of providing a coverage area of a cell less than 10 m in radius.
In the meantime, the femtocell adopts a concept of a Closed Subscriber Group (CSG). Accordingly, the femtocell makes a control such that only a CSG can access thereto. The femtocell is generally operated in a CSG mode and provides services only to terminals included in the CSG. The femtocell operated in the CSG mode is referred to as a CSG cell hereinafter.
In order for user equipment to enter the CSG cell, the femtocell performs a control of an access. To this end, the user equipment is required to have a list of CSG cell identifications, i.e. an allowed CSG List (ACL) of the user equipment, which corresponds to CSG cells the user equipment has a right to access.
In the meantime, a handover, which is one of the most remarkable characteristics of the wireless communication system using a cellular network, is required in order to secure a mobility of the user equipment. Since a plurality of femtocells may be installed within one macrocell area, the handover is performed when the user equipment moves between the macrocell and the femtocell. The entrance of the user equipment to the femtocell from the macrocell is referred to as an inbound handover, and the entrance of the user equipment to the macrocell from the femtocell is referred to as an outbound handover.
Contrary to the outbound handover, in a case of the inbound handover, a network identifies if the user equipment belongs to the femtocell, i.e. a CSG of a CSG cell. Only when the user equipment belongs to the CSG of the CSG cell, the network may initiate a handover preparation procedure. That is, before the performance of the handover to the CSG cell, the network should perform a control of an access of the user equipment.
A specific method of performing an inbound handover by the user equipment has not been currently defined. Accordingly, a method of efficiently performing the inbound handover by a user equipment has been demanded.